A press-type liquid pump is generally installed at an opening of a container, for pumping and dispensing a liquid product in the container to the exterior thereof by means of a manual pressing operation by a user for later use. This liquid pump generally has an elastic restoring means for restoring a pump pressing head to an original position thereof after the user has removed the downward pressing force on the pressing head, and during the restoring of the pressing head, the liquid product within the container is sucked into a liquid reservoir of the liquid pump for pumping and dispensing by the next pressing.
In conventional press-type liquid pumps, the elastic restoring means is generally fitted between a movable unit (generally including a pressing head and a piston rod) and a fixed unit (generally including a cylinder) in a pre-loaded manner, so as to ensure that there is enough elastic force to enable the movable unit to be restored to the original position thereof relative to the fixed unit after the user has removed the downward pressing force. However, keeping the elastic restoring means in a loaded state for a long time would result in creeping and fatigue failure of the elastic means, ultimately resulting in an insufficient rebounding force to restore the movable unit into position, and thereby influencing the amount of liquid outputted by the liquid pump.
Furthermore, the conventional press-type liquid pumps mostly use a metal spring as the elastic restoring means, as shown in FIG. 49. The metal spring 1010 for use in this liquid pump rusts easily due to damp or contact with liquid, and a rusted spring affects the quality of the product (including the quality of the spring and the quality of the liquid product in the container). Moreover, the cost of the metal spring is relatively high, and in the recycling of the liquid pump, the metal spring needs to be disassembled from other plastic members for separate recovery, which greatly increases the cost of recovery.
Another press-type liquid pump is a bellows type plastic spring pump, as shown in FIG. 50, which uses an elastic force generated by the bellows 1110 when deformed to provide the power force for the restoring movement of the press-type liquid pump. However, this bellows type plastic spring inherently presents the problem of an insufficient elastic force, which, in the case that the liquid product is relatively viscous or a relatively high amount of liquid to be pumped out is required, will inevitably make a rebound difficult or even impossible, thereby affecting the use by consumers. Furthermore, in order to enable such a liquid pump to rebound into position during use, the bellows must be installed in a pre-loaded manner such that it has been subjected to a certain pre-stressed deformation before use; however, after it has been in place for a long time or due to changes in the ambient temperature, the bellows spring is prone to creeping, resulting in the previously stored elastic deformation disappearing, thereby resulting in a reduced rebounding force.
A further press-type liquid pump is a neck casing type plastic spring pump, as shown in FIG. 51 and as disclosed in U.S. Pat. No. 6,223,954. A disadvantage of the spring 1210 used in this liquid pump is that a very large downward pressing force is required to bend the spring when the pressing head is in the vicinity of an upper stop position of a pressing stroke, and the rebounding force that can be provided by this plastic spring is too small when the pressing head is in the vicinity of a lower stop position of the pressing stroke, resulting in a slow or incomplete restoration. Moreover, in terms of the appearance, the casing type spring is arranged above the toothed sleeve of the liquid pump, making the section above the toothed sleeve particularly bulky and even larger after a downward pressing, which is very unattractive.